If it is possible to obtain single crystal ferromagnetic thin films exhibiting high ferromagnetic characteristics while transmitting light, it will be possible to provide light isolators or to perform high-density magnetic memory as it is required in transmitting a large amount of information and thus to manufacture electronic materials required for transmission of large amount of information in the future. It is therefore being wanted for materials exhibiting ferromagnetic characteristics while transmitting light.
On the other hand, ZnO-type compounds are advantaged through their characteristics of exhibiting a large band gap of 3.3 eV and transmitting light of wavelengths ranging from blue to ultraviolet, and due to their large binding energy of their excitons when compared to, for instance, GaN, remarkable progresses are being expected in the field of manufacturing optical devices such as light quantum computers employing coherent spin states once it is possible to exhibit ferromagnetism through these materials. However, while there are conventionally known cases in which ZnO is doped using Mn, ZnO will be in an antiferromagnetic state and no cases have so far been reported in which ZnO-type compounds are in ferromagnetic conditions.
As noted, if it would be possible exhibit ferromagnetic characteristics by using ZnO-type compounds, quite a large variety of applications to devices utilizing magnetic-optical effects will be provided in which these compounds are used in combination with light-emitting elements such as semiconductor laser of ZnO-type compounds exhibiting large binding energy of excitons or in which light reflecting magnetic states are generated.
In case of arranging memories of ferromagnetic bodies by irradiating such light and varying magnetic states, it will be necessary to set ferromagnetic characteristics to be desired ones in which, for instance, a ferromagnetic transition temperature (Curie temperature) is set to be a temperature that is varied upon radiation of light (a temperature slightly higher than room temperature).